The present invention relates to a thrust roller bearing assembly mainly used in an automatic transmission of an automobile.
Helical gears are usually employed in the automatic transmission in order to ensure a smooth transmission of rotations. But, because an axial thrust is exerted with the rotation of the helical gears, it is necessary to support the axial thrust by use of thrust bearings such as thrust roller bearings.
Meanwhile, because each finished component of the transmission has some variation in dimensions, there is necessarily some variation in the axial gap with the thrust bearing assembled. In particular, if a plurality of helical gears are mounted outside of a shaft, a substantially large variation will be produced in the helical gear assembly assembled at the last stage as a result of accumulation of the variations in the assemblies assembled at early stages. Therefore it is customary to compensate for the variation in the axial gap by using a shim of a suitable thickness.
It has hitherto been usual to measure a gap dimension L between a thrust member 20 such as helical gears and a pressure receiving member 21 as shown in FIG. 17, subtract the width B of the thrust roller bearing to be used from the dimension L, select a gap adjusting shim 30 having the nearest thickness to the calculated value out of several kinds of adjusting shims having different thicknesses prepared beforehand, and combine the thrust roller bearing A with the thrust members 20 and combining the gap adjusting shim 30 with the pressure receiving member 21, as shown in FIG. 16, and assemble the thrust member 20 and the pressure receiving member 21 together.
Since the gap adjusting shim 30 and the thrust roller bearing A are mounted separately, the assembly is very time-consuming. Moreover, because the gap adjusting shim is adapted to be supported by an engagement portion 31 formed on its inner edge so as to be received in an engagement groove 23 formed in the surface of the pressure receiving member 21, the gap adjusting shim 30 has a tendency to fall off or to cause displacement during the relative assembly of the thrust member 20 and pressure receiving member 21. This makes it more difficult to assemble the transmission system.